Soft connective tissues (e.g. tendons, ligaments, joint capsules) associated with, or spanning, a diarthrodial joint contribute to stabilizing the joint and provide the means for effecting relative motion between the bones. These soft connective tissues have a very unique morphology in terms of their insertion site into bone [Rufai et al., J Orthop Res (1995), 13:585-593; Benjamin et al., J Anat (1992), 180:327-332; Ralphs and Benjamin, Anat (1994), 184:503-509; Frowen and Benjamin, J Anat (1995), 186:417-421]. As the soft tissue structure approaches its insertion site into bone, the tissue morphology changes from a dense, regular, longitudinally aligned tissue to fibrocartilagenous tissue, to calcified fibrocartilagenous tissue, and finally to bone tissue. Additionally, the collagen fiber orientation changes rapidly from being longitudinal (i.e. along the soft tissue load-bearing direction) to being perpendicular to the calcification tidemark. This uniquely differentiated transition zone at the insertion site is typically referred to as the “enthesis.” The normal biology of the soft tissue enthesis (a) ensures a gradual transition from a soft tissue to a much stiffer bone tissue, (b) minimizes mechanical stress concentrations at the attachment site, and (c) maximizes the tendon pullout force from the bone.
Total joint replacement procedures (primary or revision) frequently result in the loss of the attachment site of these soft tissue structures due to osteotomy or simply to gain access to the joint. To fully restore joint function, these soft tissue structures have to be reattached at their anatomical (or equivalent) location around the joint. Such reattachment, however, is a challenging task since it requires mating of two very dissimilar materials i.e. a soft, biological tissue material and a much stiffer, non-biological (metallic or plastic) prosthesis.
One aspect of the present invention is directed to a composition and methodology that recreates the soft tissue enthesis morphology, as found in natural tendon, ligament, and capsular insertion sites, between the metallic implant and the soft tissue structure to be reattached to the metallic implant.